[Federal Register Volume 65, Number 51 (Wednesday, March 15, 2000)]
[Proposed Rules]
[Pages 13919-13921]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 00-6333]


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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. 99-NM-320-AD]
RIN 2120-AA64


Airworthiness Directives; Boeing Model 737-100 and-200 Series 
Airplanes

AGENCY: Federal Aviation Administration, DOT.

ACTION: Notice of proposed rulemaking (NPRM).

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SUMMARY: This document proposes the supersedure of an existing 
airworthiness directive (AD), applicable to certain Boeing Model 737-
100 and -200 series airplanes, that currently requires inspections to 
detect cracking of the support fittings of the Krueger flap actuator; 
and, if necessary, replacement of existing fittings with new steel 
fittings and modification of the aft attachment of the actuator. That 
AD also provides for an optional terminating modification that 
constitutes terminating action for the repetitive inspections. This 
action would mandate accomplishment of the previously optional 
terminating action. This proposal is prompted by reports of cracking 
due to fatigue and stress corrosion of the support fittings of the 
Krueger flap actuator. The actions specified by the proposed AD are 
intended to prevent such cracking, which could result in fracturing of 
the actuator attach lugs, separation of the actuator from the support 
fitting, severing of the hydraulic lines, and resultant loss of 
hydraulic fluids. These conditions, if not corrected, could result in 
possible failure of one or more hydraulic systems, and consequent 
reduced controllability of the airplane.

DATES: Comments must be received by May 1, 2000.

ADDRESSES: Submit comments in triplicate to the Federal Aviation 
Administration (FAA), Transport Airplane Directorate, ANM-114, 
Attention: Rules Docket No. 99-NM-320-AD, 1601 Lind Avenue, SW., 
Renton, Washington 98055-4056. Comments may be inspected at this 
location between 9:00 a.m. and 3:00 p.m., Monday through Friday, except 
Federal holidays.
    The service information referenced in the proposed rule may be 
obtained from Boeing Commercial Airplane Group, P.O. Box 3707, Seattle, 
Washington 98124-2207. This information may be examined at the FAA, 
Transport Airplane Directorate, 1601 Lind Avenue, SW., Renton, 
Washington.

FOR FURTHER INFORMATION CONTACT: Greg Schneider, Aerospace Engineer, 
Airframe Branch, ANM-120S, FAA, Seattle Aircraft Certification Office, 
1601 Lind Avenue, SW., Renton, Washington; telephone (206) 227-2028; 
fax (206) 227-1181.

SUPPLEMENTARY INFORMATION:  

Comments Invited

    Interested persons are invited to participate in the making of the 
proposed rule by submitting such written data, views, or arguments as 
they may desire. Communications shall identify the Rules Docket number 
and be submitted in triplicate to the address specified above. All 
communications received on or before the closing date for comments, 
specified above, will be considered before taking action on the 
proposed rule. The proposals contained in this notice may be changed in 
light of the comments received.
    Comments are specifically invited on the overall regulatory, 
economic, environmental, and energy aspects of the proposed rule. All 
comments submitted will be available, both before and after the closing 
date for comments, in the Rules Docket for examination by interested 
persons. A report summarizing each FAA-public contact concerned with 
the substance of this proposal will be filed in the Rules Docket.
    Commenters wishing the FAA to acknowledge receipt of their comments 
submitted in response to this notice must submit a self-addressed, 
stamped postcard on which the following statement is made: ``Comments 
to Docket Number 99-NM-320-AD.'' The

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postcard will be date stamped and returned to the commenter.

Availability of NPRMs

    Any person may obtain a copy of this NPRM by submitting a request 
to the FAA, Transport Airplane Directorate, ANM-114, Attention: Rules 
Docket No. 99-NM-320-AD, 1601 Lind Avenue, SW., Renton, Washington 
98055-4056.

Discussion

    On August 6, 1996, the FAA issued AD 96-17-04, amendment 39-9712 
(61 FR 41957, August 13, 1996), applicable to certain Boeing Model 737-
100 and -200 series airplanes, to require inspections to detect 
cracking of the support fittings of the Krueger flap actuator; and, if 
necessary, replacement of existing fittings with new steel fittings and 
modification of the aft attachment of the actuator. That action was 
prompted by reports of cracking due to fatigue and stress corrosion of 
the support fittings of the Krueger flap actuator. The requirements of 
that AD are intended to prevent such cracking, which could result in 
fracturing of the actuator attach lugs, separation of the actuator from 
the support fitting, severing of the hydraulic lines, and resultant 
loss of hydraulic fluids. These conditions, if not corrected, could 
result in possible failure of one or more hydraulic systems, and 
consequent reduced controllability of the airplane.

Actions Since Issuance of Previous Rule

    When AD 96-17-04 was issued, it contained a provision for an 
optional replacement of the aluminum support fitting of the Krueger 
flap actuator with a steel fitting, and modification of the actuator 
aft attachment, which, if accomplished, would constitute terminating 
action for the required repetitive inspections. That optional 
modification was to be accomplished in accordance with Boeing Service 
Bulletin 737-57-1129, Revision 1, dated October 30, 1981, as revised by 
Notices of Status Change 737-57-1129NSC1, dated July 23, 1982; 737-57-
1129 NSC2, dated April 14, 1983; and 737-57-1129 NSC 3, dated May 18, 
1995. Revision 1 of the service bulletin contained a provision for 
operators to replace the existing aluminum support fitting of the 
Krueger flap actuator with a new aluminum support fitting. This action 
would mandate replacement of the aluminum support fitting with a steel 
fitting in accordance with Boeing Service Bulletin 737-57-1129, 
Revision 2, dated May 28, 1998. Revision 2 of the service bulletin 
specifies replacement of the aluminum support fitting with a steel 
fitting only, all references to replacement with an aluminum support 
fitting have been removed from the service bulletin.

Explanation of Requirements of Proposed Rule

    Since an unsafe condition has been identified that is likely to 
exist or develop on other products of this same type design, the 
proposed AD would supersede AD 96-17-04 to continue to require 
inspections to detect cracking of the support fittings of the Krueger 
flap actuator on each wing; and replacement of any existing aluminum 
fitting with a new steel fitting and modification of the actuator aft 
attachment.

Differences Between Proposed Rule and Service Bulletin

    Operators should note that, although the service bulletin 
recommends that the initial inspection be performed using a visual 
method and subsequent repetitive inspections be performed at regular 
maintenance intervals using an eddy current technique, this proposed AD 
would require that both the initial and repetitive inspections be 
accomplished using the eddy current method. The support fittings of the 
Krueger flap actuator on each wing are susceptible to stress corrosion 
cracking, and the crack growth rate for such cracking is unknown. The 
FAA finds that, if a visual inspection is accomplished to detect 
cracking of the support fittings, such cracking may not be detected in 
a timely manner to adequately address the unsafe condition. Therefore, 
the FAA has determined that an adequate level of safety for the 
affected fleet requires that both the initial and repetitive 
inspections of these fittings be performed at intervals not to exceed 
3,000 hours time-in-service using an eddy current technique, which is a 
more reliable method for detection of cracking.
    Operators also should note that this AD proposes to mandate, within 
5 years after the effective date of this AD, replacement of any 
existing aluminum support fitting of the Krueger flap actuator on each 
wing with a new steel fitting; and modification of the actuator aft 
attachment, as described in Boeing Service Bulletin 737-57-1129, 
Revision 2, as terminating action for the repetitive inspections. 
Incorporation of this terminating action is described as optional in 
the service bulletin.
    The FAA has determined that long-term continued operational safety 
will be better assured by design changes to remove the source of the 
problem, rather than by repetitive inspections. Long-term inspections 
may not be providing the degree of safety assurance necessary for the 
transport airplane fleet. This, coupled with a better understanding of 
the human factors associated with numerous continual inspections, has 
led the FAA to consider placing less emphasis on inspections and more 
emphasis on design improvements. The proposed modification requirement 
is in consonance with these conditions.

Cost Impact

    There are approximately 727 Model 737-100 and -200 series airplanes 
of the affected design in the worldwide fleet. The FAA estimates that 
270 airplanes of U.S. registry would be affected by this proposed AD.
    The inspections that are currently required by AD 96-17-04, and 
retained in this proposed AD, take approximately 12 work hours per 
airplane (6 work hours per wing) to accomplish, at an average labor 
rate of $60 per work hour. Based on these figures, the cost impact of 
the currently required inspections on U.S. operators is estimated to be 
$194,400, or $720 per airplane, per inspection.
    The replacement and modification that is proposed in this new AD 
action would take approximately 88 work hours per airplane (44 work 
hours per wing) to accomplish, at an average labor rate of $60 per work 
hour. Required parts would cost approximately $12,226 per airplane. 
Based on these figures, the cost impact of the replacement and 
modification proposed by this AD on U.S. operators is estimated to be 
$4,726,620, or $17,506 per airplane.
    The cost impact figures discussed above are based on assumptions 
that no operator has yet accomplished any of the current or proposed 
requirements of this AD action, and that no operator would accomplish 
those actions in the future if this AD were not adopted.

Regulatory Impact

    The regulations proposed herein would not have substantial direct 
effects on the States, on the relationship between the national 
government and the States, or on the distribution of power and 
responsibilities among the various levels of government. Therefore, in 
accordance with Executive Order 12612, it is determined that this 
proposal would not have sufficient federalism implications to warrant 
the preparation of a Federalism Assessment.
    For the reasons discussed above, I certify that this proposed 
regulation (1) is not a ``significant regulatory action'' under 
Executive Order 12866; (2) is not a ``significant rule'' under the DOT 
Regulatory Policies and Procedures (44 FR 11034, February 26, 1979); 
and (3) if promulgated, will not have a significant

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economic impact, positive or negative, on a substantial number of small 
entities under the criteria of the Regulatory Flexibility Act. A copy 
of the draft regulatory evaluation prepared for this action is 
contained in the Rules Docket. A copy of it may be obtained by 
contacting the Rules Docket at the location provided under the caption 
ADDRESSES.

List of Subjects in 14 CFR Part 39

    Air transportation, Aircraft, Aviation safety, Safety.

The Proposed Amendment

    Accordingly, pursuant to the authority delegated to me by the 
Administrator, the Federal Aviation Administration proposes to amend 
part 39 of the Federal Aviation Regulations (14 CFR part 39) as 
follows:

PART 39--AIRWORTHINESS DIRECTIVES

    1. The authority citation for part 39 continues to read as follows:

    Authority: 49 U.S.C. 106(g), 40113, 44701.


Sec. 39.13  [Amended]

    2. Section 39.13 is amended by removing amendment 39-9712 (61 FR 
41957, August 13, 1996), and by adding a new airworthiness directive 
(AD), to read as follows:

Boeing: Docket 99-NM-320-AD. Supersedes AD 96-17-04, Amendment 39-
9712.
    Applicability: Model 737-100 and -200 series airplanes, line 
numbers 001 through 813 inclusive, certificated in any category.

    Note 1: This AD applies to each airplane identified in the 
preceding applicability provision, regardless of whether it has been 
modified, altered, or repaired in the area subject to the 
requirements of this AD. For airplanes that have been modified, 
altered, or repaired so that the performance of the requirements of 
this AD is affected, the owner/operator must request approval for an 
alternative method of compliance in accordance with paragraph (d) of 
this AD. The request should include an assessment of the effect of 
the modification, alteration, or repair on the unsafe condition 
addressed by this AD; and, if the unsafe condition has not been 
eliminated, the request should include specific proposed actions to 
address it.

    Compliance: Required as indicated, unless accomplished 
previously.
    To prevent possible failure of one or more hydraulic systems and 
consequent reduced controllability of the airplane, accomplish the 
following:

Restatement of Requirements of AD 96-17-04:

Repetitive Inspections

    (a) Within one year after September 17, 1996 (the effective date 
of AD 96-17-04, amendment 39-9712), perform an eddy current 
inspection to detect cracking of the support fitting of the Krueger 
flap actuator on each wing, in accordance with Boeing Service 
Bulletin 737-57-1129, Revision 1, dated October 30, 1981, as revised 
by Notices of Status Change 737-57-1129NSC1, dated July 23, 1982; 
737-57-1129 NSC2, dated April 14, 1983; and 737-57-1129 NSC 3, dated 
May 18, 1995; or Revision 2, dated May 28, 1998.
    (1) If no cracking is detected, repeat the inspection required 
by paragraph (a) of this AD thereafter at intervals not to exceed 
3,000 hours time-in-service.
    (2) If any cracking is detected, prior to further flight, 
accomplish the replacement and modification specified in paragraph 
(b) of this AD.

New Requirements of This AD:

Terminating Action

    (b) Within 5 years after the effective date of this AD: Replace 
any existing aluminum support fitting of the Krueger flap actuator 
on each wing with a steel fitting, and modify the actuator aft 
attachment, in accordance with Boeing Service Bulletin 737-57-1129, 
Revision 2, dated May 28, 1998. Accomplishment of this replacement 
and modification constitutes terminating action for the repetitive 
inspections required by paragraph (a) of this AD.

    Note 2: Replacement of the existing aluminum support fitting of 
the Krueger flap actuator on each wing with a steel fitting, and 
modification of the actuator aft attachment, prior to the effective 
date of this AD, in accordance with Boeing Service Bulletin 737-57-
1129, Revision 1, dated October 30, 1981, as revised by Notices of 
Status Change 737-57-1129NSC1, dated July 23, 1982; 737-57-1129 
NSC2, dated April 14, 1983; and 737-57-1129 NSC 3, dated May 18, 
1995; is considered acceptable for compliance with the modification 
required by paragraph (b) of this AD.

Spares

    (c) As of the effective date of this AD, no person shall install 
on any airplane any aluminum support fitting identified in the 
``Existing Part Number'' column of Paragraph 2.D. of Boeing Service 
Bulletin 737-57-1129, Revision 2, dated May 28, 1998.

Alternative Methods of Compliance

    (d) An alternative method of compliance or adjustment of the 
compliance time that provides an acceptable level of safety may be 
used if approved by the Manager, Seattle Aircraft Certification 
Office (ACO), FAA, Transport Airplane Directorate. Operators shall 
submit their requests through an appropriate FAA Principal 
Maintenance Inspector, who may add comments and then send it to the 
Manager, Seattle ACO.

    Note 3: Information concerning the existence of approved 
alternative methods of compliance with this AD, if any, may be 
obtained from the Seattle ACO.

Special Flight Permits

    (e) Special flight permits may be issued in accordance with 
Secs. 21.197 and 21.199 of the Federal Aviation Regulations (14 CFR 
21.197 and 21.199) to operate the airplane to a location where the 
requirements of this AD can be accomplished.

    Issued in Renton, Washington, on March 9, 2000.
Donald L. Riggin,
Acting Manager, Transport Airplane Directorate, Aircraft Certification 
Service.
[FR Doc. 00-6333 Filed 3-14-00; 8:45 am]
BILLING CODE 4910-13-U